An Applet is a program made up of java byte code, often written in the Java Programming Language. Applets are primarily used in conjunction with HTML pages, possibly including or referencing scripts written in JavaScript, VBScript, or another scripting language, where they are controlled by a computer program, typically a web browser displaying the HTML page or executing the script or scripts. Applets may also be controlled by other programs, in a fashion determined by the program using the Applet. In either case, Applets are used to provide functionality not present in or not allowed by a standard web browser or other program, to provide functionality already available but at significantly increased performance, to provide additional security over that provided by the web browser or other program, or to perform any additional function normally associated with Applets.
Conventional use of an Applet is to construct an HTML page, possibly including or referencing an associated script or scripts, said page referencing an Applet or Applets residing on a hard drive attached or available to a server computer attached to the Internet. The HTML page is then placed on the same or another hard drive attached or available to the same or another server computer, also attached to the Internet. The server computer or computers are configured to provide access to the HTML page and Applet (and possibly other files) to a user using a web browser or other program designed to access content over the Internet.
When the user accesses the HTML page, the HTML page is copied from the server computer over the Internet to the user's computer, where it is interpreted by the web browser. As the HTML page has been constructed to reference the Applet, the web browser transfers the Applet from the server computer over the Internet to the user's computer where the browser, or an auxiliary program such as a Java Virtual Machine under control of the browser execute, the Applet. The functions performed by the Applet are determined by the program code making up the Applet and the HTML or JavaScript that caused the browser to access the Applet. This use of an Applet is shown in FIG. 1.
FIG. 1 illustrates a client computer 110 running a web browser or other computer program 111 capable of displaying HTML and making use of a Java Virtual Machine 112. The client computer 110 has access over the Internet 120 to a server computer 130 running a web server or other computer program 131 capable of servicing requests for documents residing on one or more hard drives 132 either connected directly to the server computer 130 or available over a local network. One of the hard drives 132 contains, possibly among other files, an HTML document 133 referencing an Applet 134 also contained on the same or another of the hard drives 132.
When a user using the client computer 110 instructs the web browser 111 to access the HTML document 133, the web browser 111 requests the HTML document 133 over the Internet 120 from the web server 131. The web server 131 retrieves the HTML document 133 from the hard drive 132 containing the document and transfers it over the Internet 120 to the web browser 111. The web browser 111 then interprets the HTML document 133. Because the HTML document 133 references the Applet 134, the web browser 111 requests the Applet 134 over the Internet 120 from the web server 131. The web server 131 retrieves the Applet 134 from the hard drive 132 containing the Applet and transfers it over the Internet 120 to the web browser 111. The web browser uses the Java Virtual Machine 112 to execute the Applet 134 as determined by the HTML document 133.
As the Applet 134 is requested from the web server 131 and transferred over the Internet 120 each time the user accesses the HTML document 133, the client computer 110 must be connected to the Internet 120 (which it also must be to access the HTML document 133) and the server computer 130 and Applet 134 must be available. Should any of these not be the case, the functionality provided by the Applet 134 will not be available to the user. Even if all these conditions are met, the Applet 134 must be transferred over the Internet 120, which may take a considerable amount of time depending upon the size of the Applet 134, the type of connections the client computer 110 and server computer 120 have to the Internet 120, network congestion, and other factors.
Another conventional use of an Applet is to construct an HTML page, possibly including or referencing an associated script or scripts, said page referencing an Applet or Applets residing on a hard drive attached or available to a server computer attached to the Internet. The HTML page is then transferred to one or more user's computers over the Internet, possibly contained in an e-mail message to the user. The user then uses his or her web browser to view the page now stored locally. As the HTML page has been constructed to reference the Applet, the web browser transfers the Applet from the server computer over the Internet to the user's computer where the browser, or an auxiliary program such as a Java Virtual Machine under control of the browser, execute the Applet. The functions performed by the Applet are determined by the program code making up the Applet and the HTML or JavaScript that caused the browser to access the Applet. This use of an Applet is shown in FIG. 2.
FIG. 2 illustrates a client computer 210 running a web browser or other computer program 211 capable of displaying HTML and making use of a Java Virtual Machine 212. The client computer 210 makes use of one or more hard drives 213 either connected directly to the client computer 210 or available over a local network. One of the hard drives 213 contains, possibly among other files, an HTML document 214 referencing an Applet 233.
The client computer 210 has access over the Internet 220 to a server computer 230 running a web server or other computer program 231 capable of servicing requests for documents residing on one or more hard drives 232 either connected directly to the server computer 230 or available over a local network. One of the hard drives 232 contains, possibly among other files, an Applet 233.
When a user using the client computer 210 instructs the web browser 211 to access the HTML document 214, the web browser 211 transfers the document from the hard drive 213 containing the HTML document 214 to the client computer 210. The web browser 211 then interprets the HTML document 214. Because the HTML document 214 references the Applet 233, the web browser 211 requests the Applet 233 over the Internet 220 from the web server 231. The web server 231 retrieves the Applet 234 from the hard drive 232 containing the Applet and transfers it over the Internet 220 to the web browser 211. The web browser uses the Java Virtual Machine 212 to execute the Applet 233 as determined by the HTML document 214.
As the Applet 233 is requested from the web server 231 and transferred over the Internet 220 each time the user accesses the HTML document 214, the client computer 210 must be connected to the Internet 220 (which it need not be to access the HTML document 214) and the server computer 230 and Applet 233 must be available. Should any of these not be the case, the functionality provided by the Applet 233 will not be available to the user. Even if all these conditions are met, the Applet 233 must be transferred over the Internet 220, which may take a considerable amount of time depending upon the size of the Applet 233, the type of connections the client computer 210 and server computer 220 have to the Internet 220, network congestion, and other factors.
The conventional uses of Applets suffer certain drawbacks. Among these drawbacks are the necessity of copying what may be a large file containing the Applet from a hard drive attached or available to a server computer over the Internet to a local computer; the necessity for the local computer to be connected to the Internet even if the browser or other program controlling the Applet and the HTML page or other document describing what functions the Applet should perform are local and need not be transferred over the Internet; and the possibility that access to the Applet may not be available even if the local computer is attached to the Internet, due to network congestion, the server computer or hard drive storing the Applet not being available, or other problem.
Another use of Applets exists similar to those described above, where the Applet has been cryptographically signed and is known as a Persistent Applet. Persistent Applets can be installed on a local computer, obviating the need to transfer the Applet over the Internet. However, this method also suffers certain drawbacks, among which are the difficulty in removing Persistent Applets once installed; the difficulty of updating the Persistent Applet to a newer version containing bug fixes, new functionality, enhanced security, or other modified characteristics; the difficulty in maintaining multiple incompatible versions of the Applet, for example to allow making use of legacy programs or documents requiring an older version while still allowing current programs or documents to use the most recent version; the difficulty in preparing Persistent Applets; and the requirement for a user to have Administrator privileges to install Persistent Applets on computers running certain operating systems, said privileges often not being available to users, particularly in corporate environments. For these and other reasons, Persistent Applets are rarely used in practice, despite the advantages they provide over regular Applets.